LISST-VSF

Optical Volume Scattering Function and Depolarization Sensor

World’s first autonomous, submersible instrument for measuring the volume scattering function (VSF) of water with depolarization. Measures P11, P12 and P22 elements of Mueller matrix of water. Also beam attenuation c and scattering b.

The LISST-VSF covers the angular range from 0.094 to 150 degrees. Of this, the range 0.094 to 14.9 degrees is covered with Sequoia’s 32-ring detector optics as in the LISST-200X. From 15 to 150 degrees scattering from the length of a laser is viewed by a rotating eyeball. These data produce P12 and P22.

Please click here for article on how the LISST-VSF operates. Scroll down for a video explaining operation.

The LISST-VSF comes with all the items necessary for deployment including a rechargeable NiMH external battery pack that allows more than 15 hours of continuous data collection. A test chamber is also provided to allow the instrument to be tested in the lab. An optional mixed test chamber with four counter rotating mixers is available for extensive laboratory testing.

Raw LISST-VSF data viewed using the Matlab GUI

The LISST-VSF also ships with Matlab scripts that allow for both viewing raw data and for one step data processing. Raw data from the instrument is plotted using a Matlab based GUI. This piece of software is useful for conducting quick QC checks of the data or ensuring cleanliness of the instrument and/or background water.

The Matlab processing functions handle all of the calculations required to convert raw data to the calibrated Volume Scattering Function. All that is required for processing is a raw data file and a clean water background file. The processing function returns approximately 15 different computed variables, most notably:

P11 (Volume Scattering Function)

P12

P22

Beam attenuation coefficient (c)

Scattering coefficient (b)

Depth

Temperature

Optional data plots produced by the one step data processing function

The processing function also provides the option of plotting several of the computed data products.

All of the source code for the processing functions ship with the LISST-VSF. The code can be edited for custom applications or used as a tool to better understand the steps involved in the data processing.

See article below for more details about the LISST-VSF or click here to read the abstract.

Accessories

FAQ

What does the LISST-VSF measure?

The LISST-VSF is a tool for optical oceanographers and limnologists. It measures the volume scattering function of water, the beam attenuation coefficient, and scattering coefficient. In addition, it measures the depolarization properties, P12. P22 . P22 has a ‘blind spot’ around 45 and 135-degrees.

What is P12 and P22

Any light scattering event changes the polarization state of the scattered light. Even if unpolarized light scatters off a particle, the scattered light will be partially polarized. The parameter P12 describes one of the depolarization properties of the scattering medium. P22 is an indicator of sphericity; P22=1 for spheres only. For in-depth understanding, we recommend the text: Absorption and Scattering of Light by Small Particles by C. Bohren and D. Huffman.

Does the instrument measure and record depth and temperature also?

Yes.

How is power provided?

A rechargeable external power pack is included with the instrument.

What is the angular resolution in VSF

In the small forward angles, the angle spacing is logarithmic, from 0.088 to 14.3 degrees in 32 steps. Beyond that, VSF is measured at 1-deg intervals.

How long does it take to acquire one full data set?

It takes 2 full rotations of the ‘eyeball’ to capture a single set of data. This takes about 3 seconds.

What software is included?

Software is based on Matlab, and it processes the full datafile, producing VSF, P12, P22, b, c, depth and temperature.

What do I need to learn to operate the instrument?

We have greatly simplified the user interface, and it is mostly intuitive. But, we recommend that you read the short manual in any case.

How is LISST-VSF different from previous VSF sensors?

LISST-VSF has these capabilities that prior sensors did not: (1) It measures small-forward angle VSF, from 0.09-deg out to 150; (2) It measures beam-c accurately with a beam acceptance angle < 0.06-degrees. (3) It measures P12 and P22 from 15-150 degrees; (4) From the VSF, it derives an estimate of beam-scattering coefficient b. (5) It is programmable and autonomous, ready for profiling or fixed use. (6) Laboratory use is easy, with a provided sample chamber.